#include<iostream>
#include<iomanip>
using namespace std;

int main()               //给两个电阻，求并联电阻
{
    double r1,r2;
    cin >> r1 >> r2;
    double R = 1.0/((1.0/r1)+(1.0/r2));
    cout << fixed << setprecision(2) << R << endl;
    return 0;
}